It is sometimes a matter of ecological policy depending on drought conditions. During some drought times (and I fear we are entering another) it is the policy not to automatically give water but will if asked. It isn't just the amount of water consumed (or not) but the dishwashing water and energy.

Ironically, I have to ask for water when eating in a high-end classy restaurant. But if I'm just going to some hole-in-the-wall retaurant, they serve water right away. Maybe the more expensive ones assume you're going to order wine?